The present invention is directed to semi-crystalline polyester/low viscosity polyethylene melt blends, which are more readily grindable by cryogenic grinding techniques to provide powders that are suitable for powder adhesives or powder coating materials, the powder adhesives being particularly suitable for fusible-interlinings; and to a process for making the powder.
Certain semi-crystalline polyesters are useful as fusible interlining adhesives and as powder coating materials. Cryogenic grinding of the polyesters into powder and subsequent powder classification is relatively expensive because of the difficulty in grinding them into powders.
A fusible interlining is a fabric which has been coated on one side with a discontinuous pattern of fusible adhesive. When the interlining is bonded to a base fabric in a garment, it provides body and shape to the garment without impairing the ability of the fabric to breathe. Fusible interlinings are used in the manufacture of men's and women's suits, in shirt collars and cuffs, and in the waistbands of trousers.
Certain polyamide terpolymers are currently being used as fusible interlining adhesives. The polymers used are generally terpolymers containing nylon 6, 66, and nylon 10, 11, or 12 units in the terpolymer. These polymers generally melt at about 100.degree. C. and are used in the form of fine powders. Although used commercially, these polyamide powders have certain deficiencies. For example, polyamides absorb large amounts of moisture and they block in the presence of high relative humidity conditions. Therefore, they must be stored in polyethylene lined bags prior to being used.
Polyamides also have inadequate bond strength on rainwear fabrics, and they tend to strike through on dark fabrics giving them an undesirable appearance.
Certain copolyesters are potentially useful for fusible interlinings applications which do have adequate bond strength on rainwear fabrics and which do not tend to strike through on dark fabrics, but powdering of these copolyesters by cryogenic grinding techniques is relatively expensive.
It has now been found that melt blending of small amounts of low-viscosity polyethylenes with these polyesters or copolyesters results in substantially improved grinding rates and, therefore, substantially decreases the cost of manufacturing powder. These melt blends were found to provide non-tacky and non-blocking blends, readily reduced to powder by cryogenic grinding techniques. The yields of powder were also found to be substantially higher than those obtained when grinding the non-blended polyester or copolyester.
Such low viscosity polyethylene useful in the practice of this invention include both low- and high-density polyethylene materials. Such polyethylenes may also be unmodified or chemically modified by oxidation or grafting.
Polyesters or copolyesters useful in this invention include materials having melting points in the range of about 80.degree.-175.degree. C. with inherent viscosities of about 0.4 to 1.2.
An object of the invention, therefore, is to provide polyester/low- and high-density polyethylene melt blends, which are more readily grindable by cryogenic grinding techniques, for providing powders which are useful as adhesives or powder coating materials.
Another object of the invention is to provide an economical method for obtaining polyester/low- and high-density polyethylene melt blend powders which are particularly useful as fusible interlining adhesives for use in rainwear,, men's and women's suits, shirts, and trousers.